Roundcube Webmail: Insufficient CSS sanitization in HTML e-mail messages

Description

An issue was discovered in Roundcube Webmail 1.6.0 before 1.6.14. Insufficient Cascading Style Sheets (CSS) sanitization in HTML e-mail messages may lead to SSRF or Information Disclosure, e.g., if stylesheet links point to local network hosts.

Basic information

Type
reviewed
Severity
medium
Advisory on GitHub
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Repository advisory
Source code
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Published (advisory)
2026-04-03 06:31:32 UTC
Updated
2026-04-04 06:53:58 UTC
GitHub reviewed
2026-04-04 06:53:55 UTC
NVD published
2026-04-03 05:16:22 UTC

EPSS Score

Score Percentile
0.04% 13.26%

CVSS Scores

Base score Version Severity Vector
5.4 3.1
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:C)
Breaking this can reach past the original component and bite other resources—bigger blast radius.
Confidentiality (C:L)
Some sensitive info could get out, but not a total data dump.
Integrity (I:L)
Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N)
Service keeps running; no real outage angle.

Identifiers

CWEs

CWE id Name
CWE-669 Incorrect Resource Transfer Between Spheres
CWE-918 Server-Side Request Forgery (SSRF)

Affected packages (1)

Vulnerable version ranges and first patched releases as published by GitHub.

Ecosystem Package Vulnerable range First patched Vulnerable functions
composer roundcube/roundcubemail >= 1.7-beta, < 1.7-rc5 1.7-rc5

References

cvelogic Threat Intelligence